The purpose of oil well safety valves is to automatically stop production of the effluent in case of an accident at the head or downstream of these valves. The valves controlled hydraulically from the surface to open and automatically close by means of a strong return spring the moment there is a drop in hydraulic pressure, whether controlled or accidental. These valves have been the object of much research concerning development and improvements, and they are widely used in particular in offshore wells.
In order to facilitate understanding the invention, it is assumed in the following description that the valves assume the positions corresponding to those they have in an oil well, the terms "high", "low", "upper", "lower" referring to such positions.
Essentially such valves comprise a valve body of generally tubular shape, provided at the lower part with a compensating or balancing gate issuing into the balancing chamber, a movable ball or flap shutter which, in the closed position, separates the balancing chamber from the lower end of the overall valve, called the valve "tip", the shutter being spring-biased toward the closed position, a tubular slide housed in the valve body for opening the shutter when descending or moving downwardly, a return spring designed to bias the slide toward a higher position corresponding for closing the shutter, hydraulic displacement means for moving the slide downward to push the shutter toward the open position, and a holding system located at the higher part of the valve body to fix the overall valve in the production pipe (which for that purpose is provided with a suitably shaped receiving sleeve).
Presently such valves are tested at the surface by inserting them into a production pipe which is pressurized in such a manner as to simulate actual operating conditions. However these tests require substantial time and are difficult to carry out, and furthermore, when a leak is detected, do not permit locating the defect. As a result the operator haphazardly carries out repairs either on the flap system and its tightness or on the compensating system and its tightness.
Accordingly, a primary object of the present invention is to overcome these drawbacks by creating a specific cell for testing the seals of the oil well safety valves.
Another object of the invention is to make it possible to carry out these tests in substantially less time by means of operations which are greatly simplified.
Another object is to allow immediate location of any defect.